In recent years, semiconductor devices have become smaller and smaller, and device structures have accordingly become more complicated. The process of planarizing the semiconductor wafer surface is assumed to be a very important process in fabrication of the semiconductor devices. A typical technique for use in the surface planarization is chemical mechanical polishing (CMP). In the chemical mechanical polishing, a polishing liquid containing abrasive particles such as silica (SiO2) is supplied to the polishing surface of a polishing pad, and a semiconductor wafer is in sliding contact with the polishing surface, to thereby polish the surface of the semiconductor wafer. The polishing pad may be replaced with a fixed abrasive pad made by bonding the abrasive particles by a binder.
The chemical mechanical polishing is performed using a CMP apparatus. A typical CMP apparatus includes a polishing table having a polishing pad attached to an upper polishing surface thereof, and a top ring for holding a substrate such as a semiconductor wafer, which is a workpiece to be polished. While the polishing table and the top ring are rotated about their respective own axes, the top ring presses the substrate against the polishing surface (upper surface) of the polishing pad at a predetermined pressure and a polishing liquid is supplied to the polishing surface, to thereby polish the substrate surface to a flat and mirror finish. A typical polishing liquid is an alkali solution having fine abrasive particles such as silica suspended therein. The substrate is polished by a combination of a chemical polishing action by the alkali and a mechanical polishing action by the abrasive particles.
When the substrate is polished, the abrasive particles and polishing debris adhere to the polishing surface of the polishing pad. As a result, characteristics of the polishing pad are changed and the polishing capability is lowered. For this reason, as the substrate polishing is repeated, the polishing rate is lowered and uneven polishing occurs. Thus, in order to condition the polishing surface of the deteriorated polishing pad, a dressing device is provided adjacent to the polishing table.
A typical dressing apparatus includes a rotatable dresser head and a dressing member secured to the dresser head. While the dresser head is rotated about its own axis, the dressing apparatus presses the dressing member against the polishing surface of the polishing pad on the rotating polishing table, to thereby remove the abrasive liquid and the cutting debris from the polishing surface and planarize and condition (dress) the polishing surface. A typical dressing member is a workpiece having diamond particles electrodeposited on a surface (dressing surface) in contact with the polishing surface.
Note that the polishing surface of the polishing pad is worn due to polishing of a specific number of substrates and due to the dressing as described above. Thus, when the wear of the polishing pad reaches a certain level, the polishing pad needs to be replaced. The substrate cannot be polished in a state in which the polishing pad is worn, and thus it is necessary to determine an appropriate replacement timing of the polishing pad.
In light of this, in order to detect wear of a polishing, namely, an appropriate replacement timing of the polishing pad, there is known a technique of estimating the service life of the polishing pad based on the rotation speed or the rotation torque of an electric motor for a pad conditioning assembly (see National Publication of International Patent Application No. 2007-529111).
In addition, there is known a technique of detecting rotation torque, sweep torque, and other torque of a conditioning disk for dressing, and then detecting wear of a polishing pad based on the detected values (see National Publication of International Patent Application No. 2011-530809).
However, the CMP device may encounter the need to replace the polishing pad when the entire surface of the polishing pad is worn and uneven wear occurs before the useful service life has elapsed. For example, when the polishing pad is attached to the polishing table of the CMP device, air (bubbles) may be mixed between the polishing table and the polishing pad, resulting in that a mixed air portion of the polishing pad slightly rises with respect to the polishing table. Note that although not limited thereto, some unevenness may occur on the surface of the polishing pad due to other causes. When chemical mechanical polishing is performed on the substrate or dressing is performed on the polishing pad in such a state, the contact pressure of the raised portion of the polishing pad is stronger than that of other portions, causing wear, that is, whereby uneven wear occurs. The chemical mechanical polishing performed on the substrate in the state in which uneven wear occurs on the polishing pad may reduce the planarization of the polished substrate and the polishing rate.
Furthermore, there is known a technique of detecting a frictional force or an impact force occurring between a pad dresser (dresser head) and a polishing pad of a dressing device when the polishing pad of the dressing device is dressed (see Japanese Patent Laid-Open No. 2005-022028).
Furthermore, there is known a technique for a polishing apparatus which calculates an amount of wear of a polishing pad from the height of the polishing pad and diagnoses the state of the polishing surface of the polishing pad based on the amount of wear of the polishing pad and torque or current of a polishing table rotating motor and torque or current of a top ring rotating motor (see Japanese Patent Laid-Open No. 2012-056029.
Still furthermore, there is known a technique for a dressing device which detects current flowing in a motor for rotating a polishing table having a polishing surface when the polishing surface is dressed, to thereby detect a friction load acting between the polishing surface and the dresser (dresser head) (see Japanese Patent Laid-Open No. 2006-272549).